The present invention relates to compositions containing glyceryl monolaurate (hereinafter GML) in combination with esters of para-hydroxybenzoic acid and, optionally, one or more organic surfactants. More particularly, this invention relates to the use of such compositions at ambient temperatures to clean, disinfect and preserve contact lenses, surgical or dental instruments, and other devices or formulations which contact sensitive body tissues.
For example, soft contact lenses, such as those made from plastic gel materials like hydroxyethyl methacrylate (HEMA) or its analogues and ethylene glycol dimethacrylate (EGMA) or its analogues, are replacing traditional hard contact lenses as the lenses of choice for many people. Soft lenses are more comfortable to wear than the hard lenses, but they pose a more complex problem than the hard lenses when it comes to care and maintenance. Hard lenses may be cleaned and disinfected relatively easily. Since they do not absorb appreciable amounts of water and aqueous solutions, the use of harsher cleaning and disinfecting agents is not generally a problem.
Soft lenses, on the other hand, require greater care in cleansing and storage. The solutions useful with hard lenses generally are not considered compatible with soft lenses because the soft lenses tend to absorb or concentrate certain constituents of the formulation, which could result in damage to the lens or harm to the eye of the user.
Similarly, soft lenses are more vulnerable to microbial contamination than are hard lenses. The nutritive effect of body fluids, and the protective effect of nicks or imperfections in the soft lens, can serve to augment the growth of microbes.
While it is relatively easy to find anti-microbial agents active against such microbial contaminants, it is more difficult to find an anti-microbial agent that is compatible with soft contact lenses, and more difficult yet to find one that is non-irritating and safe for contact with the human eye.
Anti-microbial agents which are suitable for external contact or even for injection or ingestion are often unsuitable for use in eye care due to the particularly sensitive nature of the tissues in the eye. For example, they might be unsuitable because of direct toxicity to the eye, poor solubility in aqueous vehicles, eye irritation or ocular allergenic effects, absorption or binding by the contact lenses, or chemical interaction with the contact lens or even its plastic lens case.
An anti-microbial agent useful for ocular applications must avoid each of the above problems. It must in particular satisfy two basic requirements, i.e. that it be non-irritating to the eye, and that it be effective against a wide variety of microorganisms. Preferably, it must be effective against a panel of six microorganisms recommended by the U.S. Food and Drug Administration (FDA).
In the past, several attempts have been made to provide solutions which could be used to clean, disinfect and preserve soft contact lenses as well as be non-irritating to the eye, non-allergenic and still effective against a wide variety of microorganisms.
The majority of solutions currently approved by the FDA for use with soft contact lenses contain either no preservative at all, or contain one such as sorbic acid, thimerosal, chlorhexidine or quaternary ammonium compounds. (See, for example, American Pharmacy, Vol. NS21 (1981) p. 19).
Such formulations have various drawbacks associated with them. Chlorhexidine, for example, can be absorbed by the soft lenses and subsequently eluted from the lenses into the eye, possibly causing irritation or burning. In addition, this compound has been shown to cause allergic reactions in certain persons. Similarly, thimerosal, another ingredient used widely in contact lens cleaning and disinfecting solutions, can cause irritation or allergic reactions, probably because it is a mercury-containing compound. Quaternary ammonium compounds have also been found to be irritating to the eye or cause an allergic response in some situations.
The choice of formulations suitable for contact lens cleaning and disinfecting solutions therefore, is limited in large part by the choice of anti-microbial agent or agents employed. While a large number of anti-microbial compounds is known, relatively few can meet the stringent requirements of reasonable concentrations, effectiveness, and lack of harmful side effects necessary in an application as demanding as a cleaning and disinfecting and preserving composition for use with contact lenses.
The present invention provides both a composition and a method for the cleaning, disinfecting and preserving of contact lenses which overcomes the disadvantages associated with currently existing solutions. The composition and method is effective against a wide range of microorganisms within a suitable period of time, and is essentially non-allergenic and non-irritating to the eye. Furthermore, the compositions of the present invention can involve the use of an essentially non-irritating surfactant. While the present invention is particularly useful with soft contact lenses, it is also useful with hard contact lenses such as polymethyl methacrylate lenses or hard gas permeable lenses such as silicone acrylate or cellulose acetate butyrate lenses.